The mechanism of control of specific arginine biosynthetic enzyme synthesis in Escherichia coli by L-arginine and by the amino acid analogue, L-canavanine, is under study. The level of mRNA specific for the ArgECBH gene cluster is being measured by DNA-RNA hybridization during phases of physiologic repression and derepression. Combining this method with study of arginine enzyme synthesis (translation), we are studying the role of tRNAarg in repression using argS mutants. The in vitro isolation and characterization of the argR protein is under study using specific binding of P32/08O darg ECBH-DNA to protein fractions. The role of arginine and arginyl-tRNA in in vitro binding of repressor to DNA as well as in the transcription of arg-mRNA from DNA are under study.